Intermittent cancer pain: clinical importance and an updated cancer pain classification

We report the characteristics of intermittent cancer pain. In addition, we propose a new clinically based classification.

Consecutive patients with cancer referred to our palliative medicine service were consented and underwent a comprehensive pain evaluation including available laboratory and radiological studies, at the time of initial contact.

In total, 100 consecutive patients reported 158 different pain sites. Pain temporal pattern observed was 60% of patients had continuous (CP) plus intermittent pain (IP); 29% IP alone; and 11% CP alone. The etiology of IP was somatic (58%), visceral (24%), neuropathic (7%), and mixed (11%). Median duration of IP was 4 months with a median daily frequency of 4 episodes. Consequently, we propose that IP be classified into IP alone or nonbreakthrough pain (NBP; because there is no underlying CP or around-the-clock [ATC] opioids used) and breakthrough pain (BP; because there is underlying CP or/and ATC opioids used). We propose that both BP and NBP be each subclassified into 3 categories: (1) incident, (2) non-incident, and (3) mixed. In addition, a 4th category exclusive to BP: end-of-dose failure. Incident pains made up (N = 42, 47%) nearly half of all IP. According to our classification, incident pain was part of BP in 41% (N = 25) or NBP in 58% (N = 17). Incident NBP received less treatment than incident BP, and it was less controlled.

(1) Intermittent pain is a major problem in patients with cancer, (2) NBP is a common but under-recognized form of cancer pain, (3) NBP is less defined and controlled than BP, (4) incident NBP accounts for 40% of all incident cancer pain, and (5) variable IP definitions and classifications make comparisons between studies difficult.